This invention relates to forced air ventilation systems and, more particularly, to improved apparatus and method for installing a secondary duct to a main duct in such a system.
In a forced air ventilation system, there is typically a main duct which is pressurized from a source of conditioned air. To distribute the conditioned air, secondary ducts are tapped into the main duct. The main and secondary ducts are typically formed from relatively thin sheet metal, generally aluminum, and their connection has heretofore not been entirely satisfactory, resulting in air leaks and not providing suitable mechanical support. It is therefore a primary object of the present invention to provide an improved structure and method for connecting a secondary duct to a main duct in a forced air ventilation system.
In the past, when connecting a secondary duct to a main duct in a forced air ventilation system, the installer would choose a location along the length of the main duct at which the connection to a secondary duct was desired. The main duct typically has at least one flat surface and the installer would, as carefully as possible, cut the sheet metal of the main duct to form an opening through the flat surface. In some installations, such as disclosed for example in U.S. Pat. No. 4,620,729, a circular opening is made and a flanged fitting is adhesively secured to the main duct by means of an intermediate resilient gasket. The secondary duct is then secured to the fitting. Such an installation is disadvantageous in that it requires a relatively expensive fitting for each secondary duct connection. A more common type of installation is effected by the installer cutting an opening, inserting the secondary duct through the opening, and sealing the opening with heavy aluminum tape designed for ductwork. This is disadvantageous in that there is minimal structural support for the secondary duct and the air seal is generally ineffective, thereby degrading the efficiency of the forced air ventilation system. The tape also has a tendency to deteriorate and allow leakage. It is therefore a more specific object of the present invention to provide structure and method for connecting a secondary duct to a main duct in a forced air ventilation system which is inexpensive, provides support for the connection of the secondary duct to the main duct, and provides an effective air seal at the connection.